Such a valve is used for example in a pump/nozzle device for supplying fuel to the combustion chamber of a cylinder of an internal combustion engine, in particular a diesel internal combustion engine. In the case of a pump/nozzle device a pump, a control unit with the valve and a nozzle unit form an assembly. A pump piston is preferably driven by way of a camshaft of an internal combustion engine by means of a toggle.
The pump can be coupled hydraulically to a low-pressure fuel supply facility by way of the valve. It is coupled hydraulically to the nozzle unit on the output side. The start of injection and the quantity injected are determined by the valve and its valve drive. The compact structure of the pump/nozzle device results in a very small high-pressure volume and a large degree of hydraulic rigidity. This allows very high injection pressures of around 2,000 bar to be achieved. This high injection pressure combined with the ease of control of the start of injection and the quantity injected allows a significant emissions reduction whilst at the same time keeping fuel consumption low when the internal combustion engines are in use.
A pump/nozzle device is known from DE 198 35 494 C2 having a pump and a valve with a valve member, which controls the hydraulic coupling of a shut-off chamber to a run-off channel. The run-off channel is coupled hydraulically to the pump and a nozzle unit. A supply channel is provided, which is coupled hydraulically to the shut-off chamber. A piezoelectric valve drive is assigned to the valve member, by way of which the valve member can be moved between two end positions. In a first end position of the valve member the run-off channel is coupled hydraulically to a shut-off chamber and this in turn is coupled to the supply channel. In a second end position of the valve member the run-off channel is decoupled hydraulically from the shut-off chamber and the valve member is in a valve seat of the valve.
In the first end position of the valve member, during a delivery stroke of the pump, fluid is taken in by the pump from the supply channel by way of the shut-off chamber and the run-off channel. During a working stroke of a pump piston of the pump, in the first end position of the valve member, fluid is pushed back from the pump by way of the run-off channel, the shut-off chamber into the supply channel. In the second end position of the valve member, during the delivery stroke of the pump piston, the absence of any hydraulic coupling between the run-off channel and the shut-off chamber and the supply channel means that no fluid is pushed back and the pump piston generates high pressure. When a predetermined pressure threshold is exceeded, a nozzle needle of the nozzle unit opens a nozzle of the nozzle unit and fluid is injected. The end of injection is determined in that the valve member is controlled by means of the actuator unit into its first end position such that fluid can flow back by way of the run-off channel into the shut-off chamber and the supply channel, with the result that the pressure in the pump and therefore also in the nozzle unit drops, which in turn causes the nozzle unit to close.
Low pollutant emissions of an internal combustion engine, in which the pump/nozzle device is disposed, a precise control of the internal combustion engine require the precise measuring in of fuel by the pump/nozzle device. This in turn requires reproducible activation of the piezocontrolled valve of the pump/nozzle device, said activation having long-term stability.